Trigger function to know which fields are being updated

["Bernard Cheung" <cheungsw@hotmail.com>]

I am writing a trigger function. How can I know which fields are being 
updated in the PL/SQL function?

For example I have a table here:

CREATE TABLE COMPANY (
  COMPANY_ID VARCHAR(10) NOT NULL,
  NAME VARCHAR(30),
  ADDRESS VARCHAR(30));

I want to write a trigger to block all update statements without updating 
NAME. I tried the following code block and it doesn't work:

  IF TG_OP = ''UPDATE'' THEN
     IF NEW.NAME IS NULL THEN
        RAISE NOTICE ' Field NAME must be provided!';
     END IF;
  END IF;

Are there any functions like the Oracle's UPDATING() predicate?

Bernard Cheung

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